A Manhattan couple died and two other people were clinging to life after being poisoned by carbon-monoxide fumes from a faulty basement furnace that forced the evacuation of scores of residents from a Murray Hill building last night, authorities said.

Firefighters raced through the six-story walkup at 535 Third Ave. at 36th Street at around 8 p.m., breaking down doors with sledgehammers to search for victims who might have been knocked unconscious by the odorless, deadly gas.

Cops said that the dead couple, who lived on the sixth floor, showed no signs of life by the time firefighters were able to force their way into the apartment.

Two other victims, who lived in separate fifth-floor apartments, were found unconscious. They were rushed to Bellevue Hospital in critical condition and then transferred to Jacobi Hospital in The Bronx, which has a hyperbaric chamber that helps increase oxygen flow.

Firefighters found one victim’s three-legged dog unconscious in an apartment and were able to resuscitate it on the sidewalk.

Some residents complained of nausea and feeling light-headed, but declined treatment.

Deputy Fire Chief James Jackson said safe carbon-monoxide readings are 9 or fewer parts per million. Ten parts per million would be dangerous, he said, adding, “The readings on the upper floors were hundreds of parts per million.”

Con Ed is looking into the possibility the tragedy was caused by a clogged furnace pipe.

On Jan. 13, a similar mishap in The Bronx took the lives of a man and his 9-year-old daughter. His wife and 12-year-old son were sickened.

The residents of the building, which has 22 units, were not allowed back inside last night.

Sunil Thadani, 37, who lives on the second floor, said, “I smelled it about 10 to 15 minutes before the firemen came. I didn’t know what it was at first. I just feel so horrible. I know I’ve seen the couple around here.”

Another resident, Alisha Davlin, who got out with her dog, Lulu, said she didn’t know what was happening until firefighters banged on her door.

“They said, ‘You have to get out!’ The firefighters were using a sledgehammer and knocking down my neighbor’s door, I guess because they didn’t know if someone had passed out.”

She said she had called the superintendent at 1 p.m. about the problem, but “he never called back.”

Karen So, another tenant, said this was not the first time residents had a problem with noxious fumes.

She said six people had to be taken to the hospital about three months ago. Con Ed officials at the scene refused to confirm there was an earlier problem.

The names of the victims were withheld pending notification of their relatives.